Precorrecting an aural carrier signal in a common amplifier system

Abstract

A circuit is provided for precorrecting an aural carrier signal in a common amplifier system in a television transmitter wherein an aural frequency signal and a visual signal are commonly amplified. The precorrecting serves to minimize cross-modulation distortion of the aural carrier caused by the common amplification. A visual carrier signal is modulated by a video baseband signal to provide a modulated video signal from which there is provided a sampled video signal. This sampled video signal is supplied to an aural corrector which provides from the sampled video signal a phase correction signal and an amplitude correction signal. The phase correction signal and amplitude correction signal are used to modulate an aural carrier signal to provide a precorrected aural signal which is then combined with the video signal to provide a combined signal.

Having described the invention, the following is claimed: 
     
       1. Apparatus for precorrecting an aural carrier signal in a common amplifier system wherein the precorrecting serves to minimize cross-modulation distortion of said aural carrier signal caused by said common amplifier system and comprising: means for receiving a modulated visual signal comprised of a visual carrier signal modulated by a video baseband signal and providing therefrom a sampled video signal;   aural corrector means for receiving said sampled video signal and providing therefrom a phase correction signal and an amplitude correction signal;   phase and amplitude modulating means for receiving said aural carrier signal and modulating same with said phase and amplitude correction signals to provide a precorrected aural signal; and   means for combining said visual signal with said precorrected aural signal to provide a combined signal.   
     
     
       2. Apparatus as set forth in claim 1 wherein said receiving means includes detecting means for detecting said modulated visual signal and providing said sampled video signal. 
     
     
       3. Apparatus as set forth in claim 2 including visual corrector means for correcting said modulated visual signal prior to application thereof to said detecting means. 
     
     
       4. Apparatus as set forth in claim 3 wherein said visual corrector means includes white level corrector means and black level corrector means. 
     
     
       5. Apparatus as set forth in claim 3 including automatic gain control means for maintaining a constant black level and located intermediate said visual corrector means and said detecting means. 
     
     
       6. Apparatus as set forth in claim 2 wherein said detecting means provides a negative video signal and inverter means responsive thereto for providing a positive video signal. 
     
     
       7. Apparatus as set forth in claim 6 wherein said aural corrector means includes positive video signal clipper adjuster means and negaative clipper adjuster means for respectively adjusting said positive video signal and said negative video signal. 
     
     
       8. Apparatus as set forth in claim 6 wherein said aural corrector means includes multiplying means for multiplying said positive and negative video signals together with the product thereof serving as said phase correction signal. 
     
     
       9. Apparatus as set forth in claim 1 wherein said aural corrector means includes video clipper means for providing said amplitude correction signal. 
     
     
       10. Apparatus as set forth in claim 9 wherein said video clipper means includes onset adjuster means. 
     
     
       11. Apparatus as set forth in claim 9 wherein said video clipper means includes slope adjuster means. 
     
     
       12. Apparatus as set forth in claim 11 including onset adjuster means and level adjuster means.